Compressor Motor Winding Switching Around Thermo-Off Events
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Solution Overview
Problem
Existing air-conditioning apparatuses face challenges in maintaining energy efficiency in low-load regions and high capacity in high-load regions while ensuring user comfort, as previous connection switching methods require compressor shutdowns, impairing comfort functions.
Innovation Solution
An air-conditioning apparatus with a connection switching device that synchronizes the switching of stator windings between star and delta connections with thermo-off events, allowing for efficient energy use without increasing compressor stop frequency, using a controller to manage the switching based on indoor temperature and thermo-off counts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the number of turns in stator windings is increased to operate on small current, then inverter losses are reduced and efficiency is improved, but induced voltage increases causing the motor to reach maximum output voltage at low rotational speed
Solution Approach 1:
The patent applies dynamic switching between star and delta connections based on operational requirements. The connection configuration is not fixed but changes dynamically - using star connection when high voltage is needed (low speed region) and delta connection when high current is needed (high speed region), thereby resolving the contradiction between efficiency at low speed and speed capability.
Solution Approach 2:
The patent changes the electrical connection parameter of the stator windings between star and delta configurations. This parameter change allows the motor to adapt its voltage-current characteristics - star connection provides higher phase voltage for low-speed operation, while delta connection provides higher phase current for high-speed operation, resolving the speed-voltage contradiction.
2Speed
If the number of turns in stator windings is decreased to operate at higher rotational speed, then induced voltage decreases allowing higher speed operation, but stator current increases causing increased inverter losses
Solution Approach 1:
The system dynamically switches connection types based on speed requirements. When high speed is needed, the system switches to delta connection which allows higher rotational speed operation. When low speed operation is required, it switches to star connection for higher efficiency, thereby resolving the contradiction between speed capability and energy loss.
Solution Approach 2:
The patent changes the stator winding connection parameter between delta and star configurations. Delta connection reduces induced voltage for high-speed operation, while star connection increases phase voltage for efficient low-speed operation, thus resolving the contradiction between speed and energy efficiency.
3Reliability
If connection switching is performed by stopping the compressor, then product safety is ensured, but compressor stop frequency increases impairing user comfort
Solution Approach 1:
The patent performs preliminary action by pre-planning connection switching to coincide with necessary compressor stops for other purposes (such as defrosting operations). By anticipating these stops and preparing the connection switch in advance, the system ensures safety requirements are met without adding extra stops that would compromise user comfort.
Solution Approach 2:
The patent merges the connection switching operation with existing compressor stop events (such as defrosting cycles). Instead of treating connection switching as a separate event requiring dedicated stops, it combines this safety requirement with operational stops that are already necessary, thereby maintaining safety while minimizing impact on user comfort.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables efficient energy use in low-load regions and high capacity in high-load regions without compromising user comfort by minimizing compressor stop frequency and improving connection switching accuracy, thus maintaining comfort and reducing unnecessary power consumption.
Implementation Method 1
a connection switching device configured to switch connection of stator windings of the electric motor between a first connection state and a second connection state higher in line-to-line voltage than the first connection state
Implementation Method 2
as an electric motor for a compressor, a permanent magnet motor driven by an inverter is in common use, where the permanent magnet motor uses permanent magnets for a rotor
Data Source
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AI summary
An air-conditioning apparatus including a compressor incorporating an electric motor; a temperature sensor configured to detect indoor temperature; a drive circuit configured to drive the electric motor; a connection switching device configured to switch connection of stator windings of the electric motor between a first connection state and a second connection state higher in line-to-line voltage than the first connection state; and a controller configured to enter thermo-off when the indoor temperature reaches a target temperature or a correction temperature set based on the target temperature and cause the connection switching device to switch connection, the thermo-off being entered by stopping the compressor via the drive circuit. When a thermo-off count reaches a reference count with the electric motor being in the first connection state, the controller causes the connection switching device to switch connection from the first connection state to the second connection state.